Meters are extensively used in the oil and gas industry to monitor and record product transfer, particularly by pipe. Such meters must be highly accurate as their readings often form the sole basis for determining the cost of goods sold and related matters such as royalties to be paid to interested parties (e.g., state and federal agencies, land owners, and investment partners). Consequently, periodic proving of the meters for accuracy is of paramount importance.
In the past, the typical procedure for proving a meter was to place a right angle drive in the meter stack between the meter and the counter (or in a more common stack of a meter, temperature compensator, and counter, between the temperature compensator and the counter). Off the right angle drive is then placed a high resolution pulser that provides the exact number of pulses per barrel passed through the meter. These pulses are then compared to the prover volume to arrive at a correction factor. This is done by comparing the actual flow through the prover volume with the reading of the pulser.
The fundamental problem overlooked by the entire industry with such methods is the location in the meter stack of the read by the right angle drive. More specifically, because the right angle drive is driven from below, the pulser reading is actually only giving a factor applicable from the right angle drive down to the meter. In other words, in determining the meter factor, the industry has assumed that all of the gear trains above the right angle take off including in the counter itself are correct and in proper working order. However, past experience has shown in particular that the counter does not always agree with the meter as when, for example, the counter gearing is wrong or has been changed out and improper gears installed or there is gear or coupling slippage due to poor connections or sheared pins. Additionally, this fundamental problem overlooked by the industry cannot simply be solved by comparing the normal counter read out with the pulser count taken below the counter because the industry itself demands more accuracy than the digit read out of the counter is capable. For example, counter read outs are typically displayed to tenths of a barrel which is commercially acceptable; however, typical pulser counts to arrive at a factor are required to be on the order of 5,000-10,000 pulses per barrel with a accuracy on the order of 3/10,000 of a barrel. Such required accuracy is literally on the order of drops of oil. Consequently, it is not enough to simply compare the digital read out of the counter with the pulses of the high resolution pulser.
With the above problems in mind, the method and apparatus of the present invention were developed. In accordance with the present invention, the final counter shaft of the counter off of which the number wheels of the counter are driven is used to prove and factor the meter stack. In this manner, the meter stack is proven and factored all the way from the meter up through the final counter shaft itself. Further, a single factor for the entire meter stack is then determined and if the factor is other than a perfect 1, it is immaterial and unnecessary to determine where in the multiple drive means and gearing of the entire stack the problem may be. Rather, the factor for the entire stack can merely be used to accurately correct any imperfection in the components of the stack from the meter up through the final counter shaft.